The integrated horizontal flux method is commonly used to estimate ammonia emission from field-applied manure. The method involves measuring the wind speed and ammonia concentration at various heights on a post in the middle of a manured plot. Wind speed and concentration profiles are subsequently fitted to these measurements. The product of the profiles represents the amount of ammonia displaced by the wind, and the calculated ammonia emission is based on integrating the product of the profiles along the height. A crucial step is the functional form of the profiles, and linear relationships employing the logarithm of the height are generally used. In this study, 160 Dutch emission experiments on grassland were re-analysed to evaluate alternative profiles for the concentration and wind speed. It is shown that an exponential concentration model usually provides a better fit than the commonly used profile and that the measurement error for the concentration should be modelled by means of a gamma distribution. Based on the re-analysis, this new model reduces the calculated ammonia emission by around 10%. It is further shown that adding a displacement parameter to the wind speed model only has a minor effect on the calculated emission. Finally, a simulation study reveals that misspecification of the concentration profile may lead to a relative bias of up to 27%, that the precision of the estimated emission can be improved by increasing the number of concentration measurements near the ground and that wind speed measurements at three heights could suffice.

中文翻译：

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用综合水平通量法估算田间施粪后的氨排放：浓度和风速剖面的比较

综合水平通量法通常用于估算田间施肥中的氨排放量。该方法包括在施肥地块中间的柱子上测量不同高度的风速和氨浓度。随后将风速和浓度分布拟合到这些测量中。剖面的乘积表示被风置换的氨的量，并且计算的氨排放基于剖面沿高度的乘积的积分。关键的一步是轮廓的函数形式，通常使用采用高度对数的线性关系。在这项研究中，重新分析了 160 次荷兰草地排放实验，以评估浓度和风速的替代剖面。结果表明，指数浓度模型通常比常用曲线提供更好的拟合，并且浓度的测量误差应通过伽马分布建模。基于重新分析，这种新模型将计算出的氨排放量减少了约 10%。进一步表明，在风速模型中添加位移参数对计算的排放影响很小。最后，一项模拟研究表明，浓度分布的错误指定可能导致高达 27% 的相对偏差，通过增加靠近地面的浓度测量次数和风速测量值可以提高估计排放的精度三个高度就足够了。